Music theory is like a guidebook to a place you haven't been before. You can wander around on your own but you probably won't see as much and you might miss some good bits. Many musicians just pick up the theory they need as they go along and never need to do any 'learning' at all, but theory can also help you speed up your musical development because it is a well trodden path that you can follow.
When I was at school I couldn't understand music theory at all. It seemed not only unbelievably complicated, but also pointless.
It shouldn't be like that.
Music theory has two purposes, communication and structure, but It only has any point if it is useful to you as a musician so, if neither purpose is useful to you, then I suggest you just keep playing and don't worry too much about it.
Music is a structure of patterns which make sense and follows a certain logic. Theory provides a way of seeing and understanding those patterns so, by taking a step along the path of understanding, you can discover a new musical structure or pattern, to put into practice. For example, imagine you want to write a song. You can work out,by ear, which of the chords that you already know go well together, and do the same to find notes to use for the melody, and you can do that every time you want to write a song. The chances are though that most of your songs could end up sounding a bit similar. However, with a little theory you can understand the pattern which determines which chords go together and which notes you can play with them. Once you see the pattern it allows you to write songs in any key because you can see which new chords you need to learn and which melody notes will go with them. Suddenly you have many more musical possibilities to explore.
Playing with other musicians
If you are playing with other people and someone says "Let's jam in G", then it's useful to know what that means. That's music theory. If your bandleader says "OK, this is in 3/4 time.", you can only do the same as everyone else if you all speak the same language. The common language that lets musicians communicate with each other is music theory so if you want to be able to play with other musicians, even a little bit of music theory will be helpful, and as you get better and need to communicate about more sophisticated musical ideas, you will find that your theory needs to also develop. But, like learning any language, it gets easier once you have some basics.
Music theory is huge. Fretmeister shows a few bits of it and how to apply those bits practically..